Exercise based cardiac rehabilitation has been shown to reduce morbidity and mortality in cardiac patients. Medical guidelines recommend performing cardiopulmonary testing prior to sending a patient home to evaluate the functional capacity of the patient. Such testing, however, is not feasible in many cardiac rehabilitation programs due to a variety of reasons such as, for example, lack of availability of such programs, feasibility for the patient, availability of secondary resources, etc. To the extent that such testing is performed, the exercise prescribed for patients is based largely upon generic heart rate guidelines that are not sufficiently tailored to the individual patient.
In some cases, physicians attempt to account for a patient's individual clinical history and symptoms. For example, a heart rate threshold for a patient may be calculated in a hospital setting for purposes of prescribing exercise. The threshold may be adjusted by the physician based upon the patient's clinical history and/or symptoms by subtracting some number such as 30 beats per minute (BPM) from the heart rate threshold. This manner of calculating heart rate threshold, however, may be overly simplistic and remains firmly grounded in general guidelines. As such, the resulting heart rate threshold does not adequately account for the patient's individual situation.
In addition, heart rate threshold for a patient is subject to change based upon changes in the health status of the patient that occur over time. Some cardiac rehabilitation guidelines, for example, recommend a target heart rate range of 60% to 80% of a predicted maximum heart rate or a 40% to 70% heart rate reserve, combined with a rating of perceived exertion (RPE) of 11-14 on the Borg scale. These quantities may be subject to change. As such, this manner of calculating heart rate threshold may have the undesirable effect of imposing variable metabolic and cardiovascular demands upon the patient.
Further complicating matters, heart rate thresholds that are indicative of exercise intensity often occur at a different percentage of maximal capacity in different patients. Hence, a group of congestive heart failure patients exercising at 50% VO2 max (e.g., the maximum rate of oxygen consumption as measured during incremental exercise) may be working at different relative intensities.